The invention relates to positive displacement machines that convert energy, namely positive displacement pumps that have continuous rotation to displace fluid contained in operating chambers. The present invention is particularly advantageous for providing balance about the various axes of the apparatus.
One of the limitations of certain types of fluid pumps is the inconsistent rotational force on the rotors caused by the force of the fluid pressure acting on the rotors as they rotate. In a gear pump, for example, the non-meshing portion of each of the gears is exposed to a consistent fluid pressure at the discharge port, but in the area where the gear teeth mesh together, each tooth on each rotor seals a tooth on the opposing rotor from the pressure of the fluid on the output side of the pump. This creates a rotationally imbalanced situation where each rotor alternates between balanced (with equal surface area exposed to the high pressure fluid on both xe2x80x9csidesxe2x80x9d of their center axis) and imbalance (with one xe2x80x9cside exposed to the high pressure fluid, and one xe2x80x9csidexe2x80x9d sealed from this high pressure fluid by a tooth on the opposing rotor). The term xe2x80x9csidexe2x80x9d refers to one half of the total surface area exposed to the high pressure fluid of the outlet port of a pump, compressor, hydraulic motor, actuator, or other related device.
The problems which result from this hydraulic rotational imbalance are mostly related to an inconsistent rotational contact force between the moving parts. As the parts rotate, the fluid force will act on each of the rotors to cause it to rotate forward or backward relative to the rotation of the other rotor. The xe2x80x9cstiffnessxe2x80x9d of the fluid film between the rotors, the inertia of the rotors themselves, and the viscosity of the fluid, are all factors which determine at what pressure and at what speed a particular pump can operate without breaking through the fluid film and causing rotor to rotor contact.
Rotor to rotor contact can be tolerated to a certain extent depending on materials and other factors, but the intermittent contact that is caused by this hydraulic rotational imbalance can cause damage or wear to the contacting parts at certain pressures and speeds and can cause damage to sensitive fluids (e.g. blood).
The higher the fluid viscosity, the xe2x80x9cstifferxe2x80x9d the fluid film, and the higher the pressure an xe2x80x9cimbalanced pumpxe2x80x9d can tolerate without contact occurring. Speed also increases the fluid film rigidity but speed also has the detrimental effect of increasing the xe2x80x9cimpactxe2x80x9d or xe2x80x9cshockxe2x80x9d characteristic of the hydraulic rotational imbalance as the pump gears (or rotors) switch back and forth from balanced to imbalanced. For certain pump configurations, it has been found that the beneficial fluid film xe2x80x9cstiffnessxe2x80x9d effects of speed is very closely counteracted by the detrimental effects of speed due to the increased xe2x80x9cimpactxe2x80x9d force.
To the best knowledge of the applicant, gear pumps, for example, are not used in many high pressure, low fluid viscosity applications due to the hydraulic rotational imbalance.
In the case of a pump such as the single face Outland(trademark) CvR(trademark) pump, the effect of any hydraulic rotational imbalance is even greater due to the high volume output and corresponding high surface area which the high pressure fluid acts on.
The most significant characteristic of apparatus of the present invention is the rotational hydraulic balancing of the slave rotor. By allowing fluid to flow past the power rotor tips at xe2x80x9cbottom dead centerxe2x80x9d (BDC) but not past the slave rotor tips at BDC. The surface area of the slave rotor which is exposed to the high pressure is within approximately 5%-10% at xe2x80x9ctop dead centerxe2x80x9d (TDC) as it is at BDC at all times. This is compared to a 100% difference between top and bottom surface areas on a pump such as the Outland(trademark) CvR(trademark) pump as disclosed in U.S. Pat. No. 5,755,196.
The rotational hydraulic imbalance is known to cause rotor to rotor contact between the Outland(trademark) CvR(trademark) rotors at approximately 500 psi with DTE Oil Light. The hydraulic rotational imbalance of the present invention is approximately 2-5% of the hydraulic rotational imbalance of the Outland(trademark) CvR(trademark) pump. This means that the pressure which could cause rotor to rotor contact with this new pump design (with DTE Oil Light) would be greater than 20,000 psi. With thicker fluids this pressure would have to be even greater.
In addition, the remaining imbalance does not occur as the rotors enter and leave the ports, but results from the movement of the contact point around the tip of the slave rotor. This reduces the xe2x80x9cimpactxe2x80x9d characteristic still further and should allow higher fluid pressures and lower fluid viscosity without contact between the rotors.
This hydraulic rotational imbalance has been accomplished by xe2x80x9cunsealingxe2x80x9d the tip of the power rotor at BDC and creating a prolonged seal between the tips of the slave rotor at BDC. This maintains a much more equal surface area between the slave rotor lobes at TDC and BDC at all times, thereby hydraulically balancing the rotors rotationally at all times. The power rotor, with this new pump design, has a consistent torquing force applied thereto as a result of the fluid pressure acting upon the radially extending surface where the full surface area of each lobe is exposed to the high pressure fluid at the outlet port at TDC but not at BDC. This pressure distribution scheme is necessary for output work to be carried out by the pump (or compressor or hydraulic motor or actuator or other related device). The important characteristic of this pump is that the slave rotor xe2x80x9cfloatsxe2x80x9d rotationally and can therefor be positioned rotationally by the fluid film of low xe2x80x9cstiffnessxe2x80x9d between it and the power rotor. Furthermore, if a fluid film does not exist due to operation conditions (drawing a vacuum, for example) the force between the rotors is low enough to be within the allowable xe2x80x9cPVxe2x80x9d value of many available materials. When an incompressible fluid is not present to establish a fluid film, it is likely that either the pressure is low enough to not create the imbalanced shock (i.e. drawing a vacuum). If there is high-pressure while a compressible fluid is present which may not establish the fluid film the presence of a compressible fluid would act as a shock absorber thereby reducing the impact effect.
Creating this hydraulic rotationally balanced characteristic has been accomplished in this new pump design by allowing fluid to flow past the power rotor tips at BDC. This is done by removing material from the slave rotor where it used to seal against the power rotor tip. A seal is maintained between the rotors in this phase of rotation by adding material to the power rotor to allow it to seal against the slave rotor tip as each slave rotor tip enters the sealed zone at BDC. This seal is maintained between each slave rotor Up and the power rotor until each slave rotor tip passes from the output port to the input port at BDC.
Further, the slave rotor can also be used as the drive rotor if a consistent contact force between the rotors is desirable. This might be the case with a single direction pump.
The invention comprises a machine that converts energy such as a pump to increase the pressure of a fluid, or a motor, turbine, or actuator taking a pressure differential in a fluid to create rotary motion about a shaft. The invention comprises a housing that has an inner surface. A first rotor is mounted for rotation in the housing about a first axis and has a first outer surface that is adapted to intimately engaged the inner surface of the housing. There is further a second rotor having a forward portion and a rearward portion and is mounted for rotation and the housing about a second axis that is offset from the first axis and being collinear by an angle a and intersects at a common center of the rotors. The second rotor has a second inner surface that defines at least part of a sphere having a common center with the center of the first rotor. There is a second outer surface that is adapted to engage the inner surface of the housing. The first rotor further has a first contact face that is defined by a locus formed by points on the second rotor as the second rotor rotates about the second axis and the first rotor further has a first contact surface positioned in the forward region of the first rotor.
The second rotor further has a second contact face that is defined by a locus formed by points on the first rotor as the first rotor rotates about the first axis. The second rotor further has a rearward surface that is positioned in the rearward portion of the second rotor. The points of each rotor that define the locus along an outer edge of a common central axis is essentially a radius extending outward from the common centers of the rotor at an angle xcex1/2 from the normal to the axis of the other rotor.
The first contact surface of the first rotor does not come in contact with the rearward surface of the second rotor allowing fluid to pass therein between.